U.S. patent application number 10/056806 was filed with the patent office on 2003-07-31 for system and method of performing an electrosurgical procedure.
This patent application is currently assigned to Medtronic, Inc.. Invention is credited to Francischelli, David, Lutterman, Alison, Mehra, Rahul.
Application Number | 20030144653 10/056806 |
Document ID | / |
Family ID | 27609329 |
Filed Date | 2003-07-31 |
United States Patent
Application |
20030144653 |
Kind Code |
A1 |
Francischelli, David ; et
al. |
July 31, 2003 |
System and method of performing an electrosurgical procedure
Abstract
A system and method of making a lesion on living tissue
including providing an electrosurgical system, determining a
desired lesion depth, selecting a power setting, and applying
electrical energy to the living tissue. The system includes an
instrument having an electrode at a distal portion thereof, and a
power source having multiple available power settings. The power
source is electrically connected to the electrode. The step of
applying electrical energy includes energizing the electrode at the
selected power setting for a recommended energization time period
that is determined by reference to predetermined length of time
information and based upon the desired lesion depth and the
selected power setting. The system preferably further includes a
fluid source for irrigating the electrode at an irrigation rate. In
this regard, the predetermined length of time information is
generated as a function of irrigation rate.
Inventors: |
Francischelli, David;
(Anoka, MN) ; Mehra, Rahul; (Stillwater, MN)
; Lutterman, Alison; (Minneapolis, MN) |
Correspondence
Address: |
DICKE, BILLIG & CZAJA
701 Building, Suite 1250
701 Fourth Avenue South
Minneapolis
MN
55415
US
|
Assignee: |
Medtronic, Inc.
|
Family ID: |
27609329 |
Appl. No.: |
10/056806 |
Filed: |
January 25, 2002 |
Current U.S.
Class: |
606/32 |
Current CPC
Class: |
A61B 18/1492 20130101;
A61B 2018/1472 20130101; A61B 2018/00351 20130101; A61B 2018/00738
20130101; A61B 2018/1253 20130101; A61B 2018/00363 20130101; A61B
2018/00577 20130101; A61B 2018/00029 20130101 |
Class at
Publication: |
606/32 |
International
Class: |
A61B 018/04 |
Claims
What is claimed is:
1. A method of making a lesion at living tissue at a target site,
the method comprising: providing an electrosurgical system
including: an electrosurgical instrument having an electrode at a
distal portion, and a power source having multiple available power
settings, wherein the power source is electrically connected to the
electrode; determining a desired depth for the lesion; selecting a
desired power setting for the power source; and applying electrical
energy to the electrode in contact with the living tissue, the
energy applied to the living tissue at the power setting for a
recommended energization time period determined by reference to
predetermined length of time information and based upon the desired
lesion depth and the selected power setting.
2. The method of claim 1, wherein the predetermined length of time
information correlates a plurality of lesion depth values with a
plurality of power setting values and identifies an energization
time period value for each lesion depth value and power setting
value combination.
3. The method of claim 2, wherein the recommended energization time
period is determined by ascertaining the energization time period
value identified by the predetermined length of time information
that otherwise corresponds with the desired lesion depth and the
selected power setting combination.
4. The method of claim 3, wherein the predetermined length of time
information is embodied in a look-up table.
5. The method of claim 3, wherein the predetermined length of time
information includes an algorithm.
6. The method of claim 3, wherein the electrosurgical instrument is
further configured to distribute a liquid from a fluid source to a
region of the electrode at a plurality of irrigation rates, and
further wherein the predetermined length of time information is
generated as a function of irrigation rate.
7. The method of claim 6, further comprising selecting a desired
irrigation rate prior to the step of applying electrical energy and
irrigating the electrode with the liquid during the step of
applying electrical energy.
8. The method of claim 7, wherein the recommended energization time
period is further determined based upon the selected irrigation
rate.
9. The method of claim 8, wherein the predetermined length of time
information includes a first correlation of lesion depth values
with power setting values for a first irrigation rate and a second
correlation of lesion depth values with power setting values for a
second irrigation rate.
10. The method of claim 9, wherein the predetermined length of time
information includes a first look-up table embodying the first
correlation and a second look-up table embodying the second
correlation.
11. The method of claim 1, wherein determining a desired lesion
depth includes: estimating a thickness of the target tissue
area.
12. The method of claim 1, wherein selecting a desired power
setting includes: considering a probability of pops during a
subsequent electrosurgical procedure.
13. The method of claim 12, wherein selecting a desired power
setting further includes: considering a probable period of time for
making the lesion.
14. The method of claim 13, wherein selecting a desired power
setting further includes: balancing a first risk associated with
the probability of pops and a second risk associated with the
probable period of time.
15. The method of claim 1, wherein the predetermined length of time
information corresponds to a length of time needed for the
electrosurgical system to create a lesion having a length of 1
cm.
16. The method of claim 1, further comprising: drawing the
electrode back and forth across the target tissue site during the
step of applying electrical energy.
17. The method of claim 16, wherein the step of drawing the
electrode back and forth results a first lesion segment upon
completion of the recommended energization time period, the method
further comprising forming a second lesion segment connected to the
first lesion segment to define a lesion pattern.
18. The method of claim 17, wherein the lesion pattern is created
as a part of a Maze procedure.
19. The method of claim 1, wherein the electrosurgical system
further includes a controller storing the predetermined length of
time information, and further wherein the recommended energization
time period is determined by: operating the controller to reference
the predetermined length of time information.
20. The method of claim 19, wherein the controller includes an
input device and a display device, and further wherein operating
the controller includes: inputting the desired lesion depth and the
selected power setting via the input device; automatically applying
the desired lesion depth and the selected power setting to the
predetermined length of time information to determine the
recommended energization time period; and displaying the
recommended energization time period via the display device.
21. The method of claim 19, wherein the controller further includes
a warning device, the method further comprising: activating the
warning device upon completion of the recommended energization time
period.
22. An electrosurgical system for performing an electrosurgical
procedure on living tissue, the system comprising: an
electrosurgical instrument having an electrode at a distal portion;
a power source having multiple available power settings and being
electrically connected to the electrosurgical instrument for
selectively energizing the electrode; and an energization look-up
table corresponding with the electrosurgical instrument, the
energization look-up table including: a power setting data set that
includes at least one of the multiple available power settings of
the power source, a lesion depth data set, energization time period
information organized as a function of the power setting and lesion
depth data sets; wherein the energization look-up table is adapted
to identify a recommended energization time period based upon a
cross-reference of a selected power setting relative to the power
setting data set and a desired lesion depth relative to the lesion
depth data set.
23. The system of claim 22, further including: a fluid source
fluidly connected to an internal lumen of the electrosurgical
instrument, the fluid source being configured to supply a liquid to
a region of the electrode at an irrigation rate during an
electrosurgical procedure.
24. The ablation system of claim 23, wherein the energization
look-up table correlates the energization time period information
with a desired irrigation rate.
25. The system of claim 22, wherein the system further comprises: a
controller electronically storing the energization look-up table,
wherein the controller is adapted to convert the selected power
setting and the desired lesion depth into a recommended
energization time period based upon reference to the energization
look-up table.
26. The system of claim 25, wherein the controller is electrically
connected to the power source, and further wherein the controller
is configured to control the power setting of the power source.
27. The system of claim 26, wherein the controller is adapted to
automatically deactivate the power source upon completion of the
recommended energization time period.
28. An electrosurgical system for performing an electrosurgical
procedure, the electrosurgical system comprising: an
electrosurgical instrument having an electrode at a distal portion;
a power source having multiple available power settings and being
electrically connected to the electrosurgical instrument for
selectively energizing the electrode; and a controller for
electronically selecting a recommended energization time period by
reference to predetermined length of time information that relates
to the electrosurgical instrument and based upon a selected power
setting and a desired lesion depth.
29. The system of claim 28, wherein the electrosurgical device
includes an internal lumen fluidly connected to at least one
passage formed in the electrode, and wherein the electrosurgical
system further includes: a fluid source fluidly connected to the
internal lumen, the fluid source being configured to supply a
liquid to the at least one passage at a selected irrigation rate
during the electrosurgical procedure.
30. The system of claim 29, wherein the controller is further
adapted to determine the recommended energization time period based
upon the selected irrigation rate.
31. The system of claim 28, wherein the controller is electrically
connected to the power source and is adapted to automatically
deactivate the power source upon completion of the recommended
energization time period.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a system and method of
performing an electrosurgical procedure using an electrosurgical
(ablation or electrocautery) device. More particularly, it relates
to a method of performing an electrosurgical procedure using an
ablation or electrocautery system to create a lesion.
[0002] A wide variety of surgical procedures involve ablation or
cauterization of selected tissue. For example, hemorrhoid or
varicose vein removal can be accomplished by ablating the tissue in
question. Additionally, tissue ablation and/or cauterization is
commonly employed for the surgical treatment of cardiac arrhythmia
and, in particular, atrial fibrillation. In general terms, cardiac
arrhythmia relates to disturbances in the heart's electrical system
that causes the heart to beat irregularly, too fast or too slow.
Irregular heartbeats, or arrhythmia, are caused by psychological or
pathological disturbances in the discharged electrical impulses
from the sinoatrial node, and the transmission of the signal
through the heart tissue, or spontaneous, unexpected electrical
signals generated within the heart. One type of arrhythmia is
tachycardia, which is an abnormal rapidity of heart action. There
are several different forms of atrial tachycardia, including atrial
fibrillation and atrial flutter. With atrial fibrillation, instead
of a single beat, numerous electrical impulses are generated by
depolarizing tissue at one or more locations in the atria (or
possibly other locations). These unexpected electrical impulses
produce irregular, often rapid heartbeats in the atrial muscles and
ventricles. As to the location of the depolarizing tissue, it is
generally agreed that the undesired electrical impulses often
originate in the left atrial region of the heart, and in particular
in one (or more) of the pulmonary veins extending from the left
atrium. With this in mind, and as an alternative to drug therapy,
ablation of the abnormal tissue or accessory pathway responsible
for the atrial fibrillation has proven highly viable.
[0003] Regardless of exact application, ablation or cauterization
of tissue is typically achieved by applying a destructive energy
source to the target tissue, including radiofrequency electrical
energy, direct current electrical energy, and the like. The
ablative energy source is provided by an electrode and is otherwise
placed in contact with the target tissue. The electrode can be
formed as part of a handheld electrosurgical instrument. As used
herein, the term "electrosurgical instrument" includes a handheld
instrument capable of ablating or cauterizing tissue. The
instrument rigidly couples the electrode tip to an instrument
handle that is otherwise held and manipulated by the surgeon. The
rigid construction of the electrosurgical instrument typically
requires direct, open access to the target tissue. Thus, for
treatment of atrial fibrillation via an electrosurgical instrument,
it is desirable to gain access to the patient's heart through one
or more openings in the patient's chest (such as a sternotomy, a
thoractomy, a small incision and/or a port). In addition, the
patient's heart may be opened through one or more incisions,
thereby allowing access to the endocardial surface of the
heart.
[0004] Once the target site (e.g., right atrium, left atrium,
endocardial surface, epicardial surface, etc.) is accessible, the
surgeon positions the electrode tip of the electrosurgical
instrument at the target site. The tip is then energized, ablating
(or for some applications, cauterizing) the contacted tissue. A
desired lesion pattern is then created (e.g., portions of a known
"Maze" procedure) and moving the tip in a desired fashion along the
target site. In this regard, the surgeon can easily control
positioning and movement of the tip, as the electrosurgical
instrument is rigidly constructed and relatively short.
[0005] Electrosurgical instruments, especially those used for
treatment of atial fibrillation, have evolved to include additional
features that provide improved results for particular procedures.
For example, U.S. Pat. No. 5,897,553, the teachings of which are
incorporated herein by reference, describes a fluid-assisted
electrosurgical instrument that delivers a conductive solution to
the target site in conjunction with electrical energy, thereby
creating a "virtual" electrode. The virtual electrode technique has
proven highly effective at achieving the desired ablation while
minimizing collateral tissue damage. Other electrosurgical
instrument advancements have likewise optimized system performance.
Unfortunately, however, use of the electrosurgical instrument to
produce a lesion having desired characteristics has remained a
lengthy and intense procedure.
[0006] Typically, a lesion is created by repeatedly drawing the
electrosurgical instrument across the target tissue site. Before,
during, and after each pass of the electrosurgical instrument
across the target tissue site, the tissue is carefully monitored
and tested to determine the depth of lesion penetration on the
target tissue site. Monitoring and testing of the site ensure the
proper number of passes of the electrosurgical instrument to create
a lesion having the desired depth for a particular procedure.
[0007] Although creating a lesion by repeatedly drawing the
electrosurgical instrument across a target tissue site is an
effective method, the need for constant monitoring and testing
increases the length of time required to perform the procedure.
Overall procedure time is critical to the safety of the surgery.
For example, a prolonged surgical treatment for atrial fibrillation
increases the length of time the heart is stopped and opened and,
consequently, increases the chance of complication and infection.
As a result, advancements are needed to decrease the time of such
electrosurgical procedures.
[0008] Electrosurgical procedures utilizing electrosurgical
instruments remain a viable method of lesion production for a
variety of surgical treatments, including the surgical treatment of
atrial fibrillation. However, typical procedures require prolonged
operation time due to the need for constant testing and monitoring
of the tissue and lesion depth. Therefore, a need exists for an
electrosurgical procedure that reduces reliance upon testing and
monitoring during the procedure, and thereby reduces procedure time
and the risk of complication.
SUMMARY OF THE INVENTION
[0009] One aspect of the present invention relates to a method of
making a lesion on living tissue at a target site. The method
includes providing an electrosurgical system, determining a desired
lesion depth, selecting a desired power setting, and applying
electrical energy to the living tissue. The electrosurgical system
includes an electrosurgical instrument having an electrode at a
distal portion thereof, and a power source having multiple
available power settings. The power source is electrically
connected to the electrode. The step of applying electrical energy
includes energizing the electrode, via the power source, at the
selected power setting for a recommended energization time period
that is determined by reference to predetermined length of time
information and based upon the desired lesion depth and the
selected power setting. In one preferred embodiment, the
predetermined length of time information is embodied in a look-up
table. In another preferred embodiment, the electrosurgical system
further includes a fluid source maintaining a supply of fluid. The
fluid source is fluidly connected to the electrosurgical instrument
and is configured to irrigate the electrode at an irrigation rate.
In this regard, the predetermined length of time information is
generated as a function of irrigation rate.
[0010] Another aspect of the present invention relates to an
electrosurgical system for performing an electrosurgical procedure
on living tissue. The electrosurgical system includes an
electrosurgical instrument having an electrode at a distal portion
thereof, a power source having multiple available power settings,
and an energization look-up table. The power source is electrically
connected to the electrosurgical instrument for selectively
energizing the electrode. The energization look-up table includes a
power setting data set, a lesion depth data set, and a
corresponding energization time period information that is
organized as a function of the power setting and lesion depth data
sets. The energization time period information is adapted to
identify a recommended energization time period for a particular
electrosurgical procedure based upon a cross-reference of a desired
power setting relative to the power setting data set and a desired
lesion depth relative to the lesion depth data set.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a side view of an electrosurgical system in
accordance with the present invention, including the portion shown
in block form;
[0012] FIG. 2 is an enlarged, cross-sectional view of a portion of
an electrosurgical instrument of FIG. 1 taken along the line
2-2;
[0013] FIG. 3 is an example of an energization look-up table in
accordance with the electrosurgical system of FIG. 1;
[0014] FIG. 4 is a flow diagram illustrating a method of use for
the electrosurgical system of FIG. 1 in accordance with the present
invention;
[0015] FIG. 5A is a cut-away illustration of a patient's heart
depicting use of the electrosurgical system of FIG. 1 during a
surgical procedure; and
[0016] FIG. 5B is an enlarged illustration of a portion of the view
of FIG. 5A.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings which
form a part hereof, and in which is shown by way of illustration
specific embodiments in which the invention may be practiced. It is
to be understood that other embodiments may be utilized and
structural or logical changes may be made without departing from
the scope of the present invention. The following detailed
description, therefore, is not to be taken in a limiting sense, and
the scope of the present invention is defined by the appended
claims.
[0018] One preferred embodiment of an electrosurgical system 10 in
accordance with the present invention is shown in FIG. 1. The
system 10 is comprised of an electrosurgical instrument 12, a fluid
source 14, a power source 16, an indifferent electrode 17, and an
energization look-up table 18. The various components are described
in greater detail below. In general terms, however, the fluid
source 14 is fluidly connected to the electrosurgical instrument
12. Similarly, the power source 16 is electrically connected to the
electrosurgical instrument 12. During use, conductive fluid is
delivered from the fluid source 14 to a distal portion of the
electrosurgical instrument 12. The distributed fluid is energized
by the electrosurgical instrument 12 via the power source 16 and
the indifferent electrode 17. The so-energized conductive fluid is
capable of forming a virtual electrode, which is capable of
ablating or cauterizing tissue. Finally, the energization look-up
table 18 is referenced to determine a recommended energization time
period for activation of the electrosurgical instrument 12 as
detailed below.
[0019] One preferred embodiment of the electrosurgical instrument
12 includes a handle 20 and a shaft 22. The handle 20 is preferably
constructed of a sterilizable, rigid, and non-conductive material,
such as polymer or ceramic. Suitable polymers include rigid
plastic, rubber, acrylic, nylon, polystyrene, polyvinylchloride,
polycarbonate, polyurethane, polyethylene, polypropylene,
polyamide, polyether, polyester, polyolefin, polyacrylate,
polyisoprene, fluoropolymers, combinations thereof, or the like.
The handle 20 forms one or more central lumens (not shown). The
lumen(s) provides a pathway for a line or tubing 24 from the fluid
source 14 to the shaft 22, as well as a pathway for a line or
wiring 26 from the power source 16 to the shaft 22.
[0020] The shaft 22 is rigidly coupled to the handle 20, and is an
elongated, relatively rigid tubular component defining a proximal
section 30 and a distal section 32. The distal section 32
terminates in an electrically conductive tip (or electrode) 34. The
tip 34 may be rounded, defining a uniform radius of curvature, or
it may have a more angular shape. In addition, the tip 34 may
comprise one or more materials and/or components. For example, the
tip 34 can have a roller ball configuration. Regardless, the
electrically conductive tip 34 shape facilitates sliding movement
of the tip 34 along the tissue.
[0021] With additional reference to FIG. 2, the shaft 22 defines an
internal lumen 28 that is fluidly connected to the tube 24 that is
otherwise fluidly connected to the fluid source 14. In this way,
fluid is delivered from the fluid source 14 to the distal section
32 via the internal lumen 28.
[0022] The distal section 32 preferably forms at least one passage
(referenced generally at 38 in FIG. 1) that is fluidly connected to
the internal lumen 28. The at least one passage 38 is formed at or
proximal to the tip 34. The at least one passage 38 provides a
relatively uniform disbursement of conductive fluid about tip 34
via the internal lumen 28. In a preferred embodiment, a plurality
of the passages 38 are provided along a circumference of the distal
section 32, as well as a passage (not shown) at the tip 34. With
this one preferred embodiment, the plurality of passages 38 are
circumferentially aligned, and uniformly spaced. Effectively, then,
the distal section 32, and in particular the tip 34, is porous.
Alternatively, the number(s) and locations(s) of the passage(s) 38
can assume any other form sufficient for distributing fluid from
the internal lumen 28.
[0023] In one preferred embodiment, the shaft 22 includes an
elongated electrode body 40 and an electrical insulator covering 42
as shown in FIGS. 1 and 2. The electrode body 40 defines the
proximal section 30 and the distal section 32 of the shaft 22. To
this end, the proximal section 30 of the electrode body 40 is
rigidly coupled to the handle 20. The insulator 42 covers a
substantial portion of the electrode body 40, preferably leaving
the distal section 32 exposed. In particular, the insulator 42 is
positioned to encompass an entirety of the electrode body 40 distal
the handle 20 and proximal the distal section 32 (and in
particular, proximal the at least one passage 38 and the tip
34).
[0024] In one preferred embodiment, the electrode body 40 is tube
formed of an electrically conductive, malleable material,
preferably stainless steel. The insulator 42 is formed of an
electrical non-conductive material and serves to electrically
insulate the encompassed portion of the electrode body 40.
[0025] Notably, the electrosurgical instrument 12 can assume a
variety of forms known in the art, varying from that described with
respect to FIG. 1. In most general terms, the electrosurgical
instrument 12 includes an electrode (e.g., the tip 34) at a distal
portion thereof. Regardless of the exact construction, the fluid
source 14 is preferably fluidly connected to the electrosurgical
instrument 12 by the tube or line 24 and maintains a supply of
conductive fluid (not shown), such as an energy-conducting fluid,
an ionic fluid, a saline solution, saturated saline solution, a
Ringers solution, etc. It is preferred that the conductive fluid be
sterile. The conductive fluid may comprise one or more contrast
agents and/or biological agents such as a diagnostic agent,
therapeutic agent or drug. In one preferred embodiment, the fluid
source 14 includes a fluid reservoir, such as a bag, bottle or
canister, for maintaining a supply of conductive fluid. With this
configuration, the fluid reservoir is positioned at an elevated
location, thereby gravity feeding the conductive fluid to the
electrosurgical instrument 12 via the tube 24. Alternatively, the
fluid reservoir may be pressurized, thereby pressure feeding the
conductive fluid to the electrosurgical instrument 12. Even
further, the fluid source 14 may include, and/or be connected to, a
manual or electric pump.
[0026] The power source 16 is electrically connected to the
electrosurgical instrument 12 by the wire or line 26 and is of a
type known in the art, preferably a radiofrequency (RF) generator.
The generator may be powered by AC current, DC current, or it may
be battery powered either by a disposable or re-chargeable battery.
The power source 16 can assume a variety of forms, and is provided
to selectively energize the electrode tip 34. To this end, the
power source 16 is preferably configured to have a multitude of
available power settings.
[0027] It will be recognized that the above-described
electrosurgical instrument 12, fluid source 14, and power source 16
are but a few examples of acceptable configurations. In general
terms, essentially any electrosurgical instrument can be used with
the present invention, and in particular in combination with the
energization look-up table 18. To this end, the success of most
electrosurgical procedures employing energized conductive fluid is
dependent upon lesion depth, power setting, irrigation rate, and
energization time. The first factor (lesion depth) is a function of
the remaining three factors that are otherwise controlled by the
surgeon. Previously, a surgeon was required to simply guess as to
appropriate settings/times for power, irrigation rate and
energization time, unnecessarily lengthening the overall procedure
time. The present invention overcomes this distinct drawback by
incorporating the energization look-up table 18, either as a
discrete table available for referral by the surgeon, or in
electronic form in a manner that assists in controlling operation
of the electrosurgical instrument 12, the fluid source 14 and/or
the power source 16.
[0028] As illustrated in FIG. 3, the energization look-up table 18
provides predetermined length of time information and is preferably
an organized collection of previously collected data correlating
the interaction between the following four variables: a lesion
depth, a power setting, an irrigation rate, and an energization
time. In general terms, the predetermined length of time
information embodied by the look-up table 18 correlates a plurality
of lesion depth values with a plurality of power setting values,
and identifies an energization time period value for each lesion
depth value and power setting value. The preferred look-up table 18
allows a user to apply two, more preferably three, of the four
variables to ascertain the fourth. Most commonly, the lesion depth,
power setting and the irrigation rate are applied to the look-up
table 18 to ascertain the corresponding energization time (or a
recommended energization time period for the particular procedure
to be performed).
[0029] In one preferred embodiment, the look-up table 18 is a
graphical representation of the four variables. An X-axis 50 of the
look-up table 18 corresponds to energization time period
information, a Y-axis 52 corresponds to a lesion depth data set,
and a first power setting data set is plotted in series 54 with
respect to the X-axis 50 and the Y-axis 52. A second power setting
data set is also plotted in series 56 and a third power setting
data set is plotted in series 58. The one exemplary look-up table
18 provides recommended energization time periods for forming a 1
cm long lesion, as described below, to the desired lesion depth at
a 95% confidence level. That is to say, a surgeon who has a desired
lesion depth and selected power setting can refer to the table 18
and ascertain a correspondingly, recommended energization time and
know that the recommended time has proven to achieve the desired
results (i.e., desired results (i.e., desired lesion depth) with a
95% confidence level. In a further preferred embodiment, the
look-up table 18 is adapted to provide energization time period
information that has a 95% confidence bound on an upper limit of
lesion depth. The one preferred look-up table 18 provided in FIG. 3
incorporates this upper bound, such that a recommended energization
time period delivered from the table 18 will not result in too deep
a lesion. Alternatively, the table 18 can be adapted to correspond
to longer or shorter lesion lengths. Further, a plurality of
different look-up tables 18 are preferably provided, with each
corresponding to a different irrigation rate and/or for different
types of tissue, such as heart tissue, liver tissue, prostate
tissue, etc. Thus, for example, a first look-up table can be
provided that embodies a correlation of lesion depth values with
power setting values, along with a second (or third, etc.) look-up
table that correlates lesion depth values with power setting values
for a second irrigation rate. Notably, the look-up table 18 may
incorporate the variables in other organizational methods (e.g.,
lesion depth versus power setting; a tabular representation of
individual lesion depth, power setting, and time period values,
etc.) and/or or need not reflect a particular irrigation rate, and
remain within the scope of the present invention.
[0030] In a preferred embodiment, the look-up table 18 is provided
apart from the electrosurgical instrument 12, such as in hard paper
form. Alternatively, a computer or similar device can be employed
to display the desired look-up table 18. In another embodiment,
however the electrosurgical system 10 further includes a controller
60. The controller 60 is preferably electrically connected to the
fluid source 14 by a line or wire 62 and to the power source 16 by
a line or wire 64, and is preferably a microprocessor-based
computer including associated memory and input/output circuiting.
Alternatively, a programmable logic controller (PLC) or other
controller or equivalent circuitry can be employed. Regardless, the
controller 60 stores the look-up table 18 and the corresponding
data sets. The controller 60 is adapted to convert two, or
preferably three variables (i.e., lesion depth, power setting,
and/or irrigation rate) inputted by a user (e.g., via a keyboard)
into a recommended energization time period value by referencing
the internal look-up table 18. The controller 60 is further
preferably adapted to adjust the irrigation rate of the fluid
source 14 and the power setting of the power source 16 as needed or
dictated by a user, and control activation/deactivation of the
power source 16 in accordance with the determined recommended
energization time period.
[0031] The flow diagram of FIG. 4 illustrates one preferred method
of forming a lesion on living tissue in accordance with the present
invention. As a point of reference, the above-described
electrosurgical system 10, including the electrosurgical instrument
12 is useful for a number of different tissue ablation and
cauterization procedures. For example, the system 10 can be used to
remove hemorrhoids or varicose veins, or stop esophageal bleeding
to name but few possible uses. Additionally, the system 10 is
highly useful for the surgical treatment of cardiac arrhythmia, and
in particular treatment of atrial fibrillation, via ablation of
atrial tissue. With this in mind, the methodology of FIG. 4 is
described in conjunction with an ablation (or lesion forming)
procedure performed on atrial tissue as shown in FIG. 5, it being
understood that the technique is equally applicable to a variety of
other electrosurgical procedures. Prior to performing the
electrosurgical procedure, it is assumed that the surgeon has
evaluated the patient and determined that the specific procedure to
be appropriate for the individual patient.
[0032] With the one preferred atrial application reflected in FIGS.
5A and 5B, a portion of a Maze procedure is performed. In
particular, FIG. 5A includes a representation of a heart 70 with
its left atrium 72 exposed. In this regard, step 100 of FIG. 4
delineates that access to a target site 74 is gained. Relative to
the one exemplary procedure of FIG. 5A, the target site 74 is
accessed by splitting the patient's sternum (not shown) and opening
the patient's rib cage (not shown) with a retractor. Various
incision are then made into the heart 70 to expose an interior of
the left atrium 72. Of course, other techniques are available for
accessing the target site 74. Further, access to a particular
target site 74 could be gained, for example, via a thoractomy,
sternotomy, percutaneously, transveneously, arthroscopically,
endoscopically, for example through a percutaneous port, stab wound
or puncture through a small incision (e.g., in the chest, groin,
abdomen, neck, or knee), etc. In addition, it is possible to gain
access to the outside of the heart 70 from within the heart 70. For
example, a catheter device may be passed from an interior of the
heart 70, through an appendage wall of the heart 70, to an exterior
of the heart 70. As described below, the electrosurgical instrument
12 may then be manipulated to contact an epicardial surface of the
heart 70.
[0033] At step 102, the electrosurgical system 10 is provided. As
previously described, the system 10 includes the electrosurgical
instrument 12, the power source 16, the fluid source 14, and the
look-up table 18. In one preferred embodiment, the system 10 also
includes the controller 60.
[0034] At step 104, a desired lesion depth is determined. To
determine the desired lesion depth, the target tissue site 74, such
as a portion of an atrial wall 75 of the heart 70 as illustrated in
FIG. 5A, is identified and evaluated to determine its thickness.
The desired lesion depth is then determined based upon the
determined thickness, as the thickness is proportionate to the
desired lesion depth. The actual proportion utilized, however,
depends upon the requirements of the particular electrosurgical
procedure being performed. For example, in an electrosurgical
procedure to correct atrial fibrillation, such as a Maze procedure,
a transmural lesion is required, and consequently, the desired
lesion depth will be equal to the thickness of the target site
tissue 74. Of course, other electrosurgical procedures may entail a
desired lesion depth that is less than the evaluated thickness of
the target site 74, for example, by a prescribed percentage (e.g.,
50% of the target site 74 thickness).
[0035] At step 106, a desired power setting for the power source 16
is selected. The power setting mandates how much heat is created
within the target tissue site 74 during a subsequent
electrosurgical procedure. As a starting point, it will be
understood that for most electrosurgical procedures, certain
recommended protocols have been developed, and are available to the
surgeon. These protocols provide guidelines or accepted ranges for
certain procedure parameters, including power setting. Thus, when
selecting a desired power setting for a particular procedure, the
surgeon will initially refer to recommended power settings. Then,
with this prescribed range in mind, to determine the specific power
setting for a particular electrosurgical procedure, the risks
associated with a probable energization time and a probability of
"pops" are considered.
[0036] A shorter ablation time generally corresponds with a lower
risk of complications, since lesions can be closed sooner, and
consequently, the body can be returned to a relatively natural
state in a shorter period of time thereby reducing the chance of
infection, thromboembolism, or other complications. Therefore,
since a higher power setting creates the lesion in a shorter period
of time, a higher power setting within the recommended range for a
particular procedure is preferred in consideration of energization
time.
[0037] However, the higher the power setting, the higher the
probability of "pops". A pop occurs when the target site tissue 74
is heated so rapidly that intracellular fluid within the target
site tissue 74 begins to boil and the target site tissue 74 erupts
causing damage to the tissue. Although a majority of the pops are
relatively small and require no further surgical intervention,
larger pops can require suturing and may thereby damage the tissue
strength and prolong the length of the electrosurgical procedure.
As a result, a goal of the electrosurgical procedure is to
minimize, or at least decrease, the occurrence of pops. Since the
higher power setting increases the probability of pops, a lower
power setting is desired in consideration of the probability of
pops.
[0038] Therefore, in selecting the desired power setting, a surgeon
considers the probable energization time and the probability of
pops to determine the power setting that will minimize the combined
risks involved in the electrosurgical procedure.
[0039] At step 108, a desired irrigation rate of the fluid source
16 is selected. The irrigation rate affects the amount and rate of
heat generated in the target tissue site 74. If the irrigation rate
is too low, the tissue will heat too quickly increasing the
probability of pops and/or causing dry
ablation/electrocauterization that may result in the build-up of
excess charred tissue on the electrode tip 34 of the
electrosurgical instrument 12, decreasing the overall performance
of the electrosurgical system 10. For example, tissue char will
raise the impedance of the tissue, thereby preventing the creation
of a deep lesion. The decreased level of performance requires the
tip 34 to be cleaned on a piece of sterile gauze or the like and,
consequently, increases the chance of incision contamination.
Conversely, if the irrigation rate is set too high, it will
overcool the target tissue site 74 increasing the time needed to
create a lesion and slow the electrosurgical procedure. As a point
of reference, ablation of atrial tissue typically entails an
irrigation rate of 3 to 10 cc/minute, more preferably an irrigation
rate of 5 ccs per minute. Of course, other procedures can have
varying irrigation rate guidelines.
[0040] Although step 108 is illustrated in FIG. 4 as following step
106, steps 106 and 108 may be performed in the opposite sequence or
relatively simultaneously.
[0041] At step 110, the predetermined length of time information
embodied in the look-up table 18 is referenced to determine a
recommended energization time period. In one preferred embodiment,
a surgeon or assistant chooses the look-up table 18 that
corresponds with the desired irrigation rate selected at step 108.
The desired lesion depth, determined at step 104, and the selected
power setting, determined at step 106, are then applied to the
look-up table 18 to determine the corresponding recommended
energization time period needed to create an appropriate lesion 76
(referenced generally in FIG. 5A) in the target site tissue 74.
[0042] In one example, the desired lesion depth is 4 mm, the
selected power setting is 25 watts, and the selected irrigation
rate is 5 cc/minute. Under these constraints, reference to the
look-up table 18 illustrated in FIG. 3 provides a recommended
energization time period of 20.7 seconds. Preferably, the
energization time information corresponds with a lesion length of 1
cm. However, the look-up table 18 can be adapted to provide
energization time period information corresponding with other
lesion lengths. Additionally or alternatively, a surgeon can
extrapolate the recommended energization time period information
for a 1 cm lesion length to arrive at an appropriate energization
time period for the particular procedure/lesion being
performed.
[0043] At step 112, the surgeon determines whether or not the
combined risks are acceptable. The surgeon compares the selected
power setting and irrigation rate previously determined at steps
106 and 108, respectively, to the recommended energization time
period determined at step 110 to ensure all values interact in a
manner that produces an acceptable combined risk of complication.
If the recommended energization time period is not acceptable based
upon consideration of the selected power setting and the resultant
procedure time, the surgeon repeats steps 106 through 112 until the
combined risks are acceptable. Once the combined risks are
acceptable, the surgeon continues to step 114.
[0044] At step 114, fluid flow from the fluid source 14 is
initiated and the power source 16 is activated, and the
electrosurgical instrument 12 (in particular the electrode tip 34)
is applied to the target tissue site 74 to create the lesion 76, as
best shown in FIG. 5B. In one preferred embodiment, liquid flow
from the fluid source 14 is initiated for a short time period prior
to activation of the power source 16 to ensure that liquid is being
distributed to the target site 74 before energy is applied. The
electrode tip 34 is then evenly drawn (preferably in a
back-and-forth motion) across the target tissue site 74 over the
length corresponding to the recommended energization time period
(e.g., 1 cm), determined at step 110, to create the lesion 76 with
the desired lesion depth. The electrosurgical device 12 may be
manipulated by a surgeon and/or by a robot. As for the previously
described example, the electrosurgical instrument 12 with the
selected power setting at 25 watts and the selected irrigation rate
at 5 cc/minute is evenly drawn across a 1 cm length of tissue for
20.7 seconds to create the lesion 76 having the lesion depth of 4
mm.
[0045] Step 114 may be repeated from an end of the newly formed
lesion 76 to form a second lesion (preferably having a length
corresponding with a length of the first lesion 76) until a number
of lesions have been created to form a desired pattern 78 for the
particular electrosurgical procedure being performed. Each lesion
segment is preferably formed at the same selected power setting and
recommended irrigation rate, utilizing the recommended energization
time period. With the one example illustrated in FIG. 5, the lesion
pattern 78 is formed on a left atrial wall 72 of the heart 70 and
encircles two right pulmonary veins 80 as a step in a Maze
procedure.
[0046] The procedure described above does not incorporate the
optional controller 60 (FIG. 1). If the electrosurgical system 10
includes the controller 60, steps 106 through 112 can be completed
by or with the assistance of the controller 60. To this end, the
controller 60 can be adapted to provide varying levels of control
over the electrosurgical instrument 12, the fluid source 14, and/or
the power source 16. For example, the controller 60 may display the
applicable look-up table 18, with the surgeon having complete,
independent control over the components 12-16. Alternatively, the
controller 60 may be adapted to automatically initiate and/or
control fluid flow from the fluid source 14 at the selected
irrigation rate. Further, the controller 60 may be adapted to
automatically deactivate the power source 16 at the completion of
the energization time. Also, the controller 60 may be adapted to
provide an audible and/or visible signal or warning (e.g., flashing
lights, buzzer, etc.) during the procedure, or at or near the
expiration of the recommended energization time period. For
example, the controller 60 may be adapted to operate a
sound-producing device in a manner that provides an audible signal
in pre-determined increments (e.g., once per second) while power is
on, thereby acting like a metronome to aid in timing the preferred
back-and-forth motion of the electrosurgical instrument 12, and in
particular the tip 34.
[0047] As previously described, the electrosurgical procedure is
highly useful for the surgical treatment of atrial fibrillation,
via ablation of atrial tissue, for example as part of the Maze
procedure. The Maze procedure, such as described in Cardiovascular
Digest Update, Vol. 1, No. 4, July 1995, pp. 2-3, the teachings of
which are incorporated herein by reference, is a well-known
technique whereby lesion patterns are created along specified areas
of the atria. The Maze III procedure, a modified version of the
original Maze procedure, has been described in Cardiac Surgery
Operative Technique, Mosby Inc., 1997, pp. 410-419, the teachings
of which are incorporated by referenced. In an effort to reduced
the complexity of the surgical Maze procedure, a modified Maze
procedure was developed in The Surgical Treatment of Atrial
Fibrillation, Medtronic Inc., 2001, the teachings of which are
incorporated herein by reference. In general terms, the system and
method of the present invention may be employed to form one or all
of the lesions/lesion patterns required by the above-identified
surgical procedures. For example, the look-up table 18 may be
referenced, and the recommended energization time period employed
to form lesions on the tricuspid annulus in the right atrium, the
coronary sinus, the mitral valve annulus in the left atrium,
etc.
[0048] The electrosurgical system and method of the present
invention provides a marked improvement over previous protocols. In
particular, by utilizing predetermined length of time information
that otherwise correlates lesion depth and power setting with
energization time, embodied by one or more look-up tables, a
surgeon can determine a recommended energization time period prior
to applying the electrosurgical instrument to the target tissue
site. Knowledge of the energization time period decreases the
requirement of constant measurement and testing during the
electrosurgical procedure and, consequently, reduces the time
required to create the lesion having the desired properties.
Reduction of the surgical time reduces the risk of complication,
accordingly.
[0049] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes can be made in form and detail without
departing from the spirit and the scope of the present
invention.
* * * * *